120 THEORY OF CONSTRUCTION AND SCIENTIFIC DESCRIPTION 



RULE. Multiply the square of the diameter of the cylinder 

 by the magnitude of the power applied, and divide the product 

 by the square of the diameter of the forcing pump, and the 

 quotient will express the intensity of the pressure on the piston 

 of the cylinder. 



125. EXAMPLE 2. If the diameter of the cylinder is 5 inches, and 

 that of the forcing pump one inch ; what is the magnitude of the 

 power applied, supposing the entire pressure on the piston of the 

 cylinder to be 18750 Ibs. ? 



Here we have given D = 5 inches; d= 1 inch, and P= 18750 

 Ibs. ; therefore, by substitution, equation (88) becomes 



5 a Xp 18750 X 1*; or p 750 Ibs. 



If both sides of the fundamental equation (88) be divided by D*, the 

 general expression for the value of p, is 



_Pd 2 



p ~ D 2 ' (90). 



And the practical rule which this equation supplies, may be 

 expressed in words at length in the following manner. 



RULE. Multiply the given pressure on the piston of the 

 cylinder, by the square of the diameter of the forcing pump, 

 and divide the product by the square of the diameter of the 

 cylinder for the power required. 



126. EXAMPLE 3. The diameter of the forcing pump is one inch, 

 and the power with which the plunger descends is equivalent to 750 

 Ibs. ; what must be the diameter of the cylinder, to admit a pressure 

 of 18750 Ibs. on the piston ? 



Here we have given c?n= 1 inch; ^ = 750 Ibs., and P n= 18750 Ibs. ; 

 consequently, by substitution, the equation marked (88) becomes 



750 D 2 =l 8750 x I 2 ; 

 hence, by division, we obtain 



consequently, by evolution, we have 

 D ^ 25 5 inches. 



If both sides of the equation (88) be divided by p, and the square 

 root of the quotient extracted, the general expression for the diameter 

 of the piston, is 



